Abstract

The reduction spots in some lithotypes of the Verrucano Group (Monticiano-Roccastrada Unit), cropping out in the central-southern Tuscany from Iano up to the M. Argentario promontory, allow us to evaluate the amount of the finite strain and to discuss the type of deformation performed during the D <sub>1</sub> phase of the Tertiary Alpine orogenesis. Generally, the reduction spots show a prolate ellipsoid shape which is related to an apparent constriction type of deformation. The parallelism between the bedding (S <sub>o</sub> ) and the D <sub>1</sub> phase foliation (S <sub>1</sub> ), the angular relationships between the ellipsoid axes and the S <sub>1</sub> foliation, and the ellipsoid shape suggest that the first Alpine deformation event developed by simple shear.